Radio communication devices such as User Equipments, UEs, are enabled to communicate wirelessly in a radio communications system, sometimes also referred to as a radio communications network, a mobile communication system, a wireless communications network, a wireless communication system, a cellular radio system, or a cellular system.
The communication may be performed, e.g., between two user equipments, between a user equipment and a regular telephone, and/or between a user equipment and a server via a Radio Access Network, RAN, and possibly one or more core networks, comprised within the wireless communications network.
Radio communication devices are also known as e.g., UEs, mobile terminals, wireless terminals, terminals and/or mobile stations, mobile telephones, cellular telephones, sensors and actuators with wireless capabilities, or laptops with wireless capability, just to mention some examples. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity.
The wireless communications network covers a geographical area which is divided into cell areas, with each cell area being served by a network node such as a Base Station, BS, e.g. a Radio Base Station, RBS, which sometimes may be referred to as e.g. eNB, eNodeB, NodeB, B node, Base Transceiver Station, BTS, access node, or access point, depending on the technology and terminology used. The base stations may be of different classes such as, e.g., macro eNodeB, home eNodeB, or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several radio access and communication technologies. The base stations communicate over the radio interface operating on radio frequencies with the user equipments within range of the base stations.
FIG. 1 shows a conventional Long-Term Evolution, LTE, protocol stack for downlink, which is used for general data communications. As shown in FIG. 1, Radio Link Control, RLC, and Medium Access Control, MAC, layers have packet manipulation, segmentation and concatenation, and retransmission functionalities. These protocol layers together pack user data into physical layer containers and take care of retransmissions in case of failed transmissions. The size of the physical layer containers and their transmission schedule, including their Transmit Time Intervals, TTIs, have to fit the basic fixed time framing hierarchy. Transmission blocks may vary in size, and they may accommodate full Internet Protocol, IP, packets, but typically they will only accommodate part of the IP packets. The transmission blocks are subject to Hybrid Automatic Repeat Request, HARQ, in case of failed delivery.
Scheduling information, such as for example, the allocation of time and/or frequency and/or antenna resources, is conveyed from a Base station, e.g. an eNodeB, to a terminal, e.g. a UE, via shared or dedicated control channels, which are closely monitored by all active terminals, e.g., all active UEs. The scheduling period, i.e., the TTI in LTE is the subframe, which is, e.g. 1 ms long. By reading the scheduling information at the beginning of each subframe, a UE may know during which time periods to receive or transmit signals.
There are further procedures in LTE and Universal Mobile Telecommunications System, UMTS, such as Discontinuous Reception, DRX, which allow less busy UEs to enter dormant cycles, when they read control channels less frequently and hereby can save battery power.
Transmission characteristics are different over wireline and mobile networks, and communications designed for IP networks do not match the protocol stack of mobile networks, which has a protocol stack that implement functionalities related to the nature of radio communications and user mobility. A typical solution to extend traditional wireline data communications to wireless nodes is to insert adaptation mechanisms between the IP protocol stack and the radio network protocol layers. That adaptation entirely hides the wireless network details for applications running over IP or similar networks. However, the interworking of wireline and wireless networks may suffer from performance degradation and inefficiency for many applications. Cross-layer optimization between the IP and mobile network protocol stacks becomes particularly important for future radio networks, which approach wireline networks in transmission speeds.
Mobile networks employ framing in their physical layers, so they have multilevel time periodicity, e.g., a hierarchy of superframes, frames, and subframes, so transmissions in either uplink or downlink directions are organized around this framing. The size of the data containers, the scheduling, and the TTIs are all matched to the given frame structure. In the transmission scheme in LTE, the IP packets are segmented on the wireless layer to fit the size in a container of physical layer transmission blocks. This means that the IP packets may need to be split up to fit in the available container set. By dividing the IP packets there is a risk that not all packets arrive successfully at the receiver, which leads to out-of sequence arrival and delays.
The wireless protocol layers in LTE barely know anything about the processes and connection states in IP level. The wireless layers might be aware of the Quality-of-Service, QoS, class and packet-delivery requirement, e.g. if in-order, lossless delivery is aimed for. But in today's mobile networks, for example, simultaneous retransmissions of the same information piece may happen over the TCP/IP and wireless layers. Also the interruptions caused by handovers can severely impact the flow control mechanisms of Transmission Control Protocol, TCP, and as a consequence, UEs cannot utilize the bandwidth that the wireless links can provide.
Scheduling information, such as the assignment of time and/or frequency and/or antenna resources, is continuously transmitted on shared or dedicated channels, which means there is power waste. Recent modifications to existing standards introduce Discontinuous Reception, DRX, and/or Discontinuous Transmission, DTX, features to provide a more power-economic mode.